The present embodiments relate to hard disk drives and are more particularly directed to a disk drive control circuit, such as may be included within a disk drive pre-amplifier, for providing voltage waveforms to drive the disk drive write mechanism.
Computer use is extremely prevalent and beneficial in today's society and has fueled ongoing efforts at improving all aspects of computer technology and design. Computers take various forms, such as the examples of desktops, workstations, or portable devices. Many of these computers include various types of storage devices, and in connection with the preferred embodiments described later, one of these devices is the hard disk drive. A hard disk drive or “hard drive” is characterized in that its read/write magnetic medium is typically not removable from the location of the read/write heads, although in some instances there may be some aspect of removability. In any event, in response to factors such as demand and competition, technology continues to strive to increase the performance of hard disk drives, such as by increasing the speed at which the drive reads and writes data relative to its magnetic disk medium. Such advancements include matters of various complexity, particularly with speeds now in the range of four gigabits per second (“Gps”). Further, various approaches of the prior art that may have proven workable in slower hard disk drives are now becoming limitations at advanced read/write speeds.
By way of further background, the disk drive write head may be electrically understood as in effect an inductor that is proximate the disk medium. Two different voltages are applied, respectively, to the two terminals of the inductor so as to generate a current through it. A generated current in a first direction writes a first binary state to the nearby disk medium, while a current generated in a second, and opposite, direction writes a second binary state to the disk medium. In generating the above-described voltages, it is known to be desirable to generate either directional current waveform to include an overshoot that is then followed by a DC component. In other words, the current waveform settles to an absolute value that is less than that of the overshoot, where that value is desired to write a corresponding binary state. Only by way of example, an overshoot of 120 mA may be generated and followed by a DC current of 40 mA to write a binary 1, while an overshoot of −120 mA may be generated and followed by a DC current of −40 mA to write a binary 0.
In connection with the preferred embodiments described later, the present inventor recognizes a limitation of prior art disk drives with respect to the waveforms that are generated to drive the drive's write head. Specifically, as drive speeds have increased, then there is a corresponding shorter period of time for the drive currents to change between writing different binary states. For example, for a 4 Gps write, each write must occur in 250 picoseconds. Thus, if a write of a binary 1 occurs in one cycle followed by a write of a binary 0 in the next successive cycle, then the voltage waveforms used to drive the head (i.e., as an inductor) must switch state in 250 picoseconds. While generating waveforms to accomplish this may be feasible in the prior art, the present inventor has observed that the change in magnetic field that occurs as a result of this fast switching of voltages may have a negative effect on the drive's nearby read head. More particularly, typically the tracer for the read head is close to the tracer for the write head. Thus, there is a coupling, or cross-talk, of the magnetic field generated by the write head tracer to the nearby read head tracer. Further, in contemporary drives the physical components of the read head may be very sensitive, and the large energy imposed on the device by the cross-talk may physically damage the read head. This cross-talk problem will likely become worse as disk drive write speeds continue to increase.
As a result of the preceding, there arises a need to address the drawbacks of the prior art as is achieved by the preferred embodiments described below.